132 



I may add that 1 am well aware that the views given above 

 are in many points open to criticism. 



The Leaf. 



Among the forms with broad leaves which persist through 

 the winter Rhododendron lapponicmn is doubtless the one that 

 is specially Arctic, and one of the oldest forms of this region; 

 consequently, it may well be the first to be dealt with. Here 

 we find a thick epidermis on both surfaces; a well-developed 

 covering of peltate hairs ; stomata especially well-protected ; 

 several layers of small palisade-cells; and a slightly branching 

 spongy parenchyma arranged in lamellae around the large inter- 

 cellular spaces. With regard to the last-named feature it may 

 be mentioned that it would be quite indefensible to connect 

 them at all with Arctic conditions such as, for example, the 

 great dampness of air in these regions. According to Lalanne, 

 leaves which may be several years' old, provided they are not 

 too small, have large intercellular spaces. This feature is not 

 dependent upon any particular climate, but should rather be 

 connected with the thickness of the epidermis, which affords 

 good protection against the danger of excessive transpiration; 

 or better still, the spaces may be rendered necessary in the 

 present instance, because the stiff, coriaceous leaves cannot be 

 stirred so freely by the wind as are deciduous leaves. 



Trying next to find a species which is as well protected 

 as Rhododendron^ we come to Ledum' This is a very common 

 species in the Arctic regions, but it has in addition a much 

 more southerly distribution, in districts with a continental cU- 

 mate, and consequently, a severe winter. It is scarcely as typi- 

 cally Arctic as Rhododendron., neither is it as old-established 

 in the region as the latter. Nevertheless it is justifiable to 

 surmise that its structure reflects to some extent the Arctic 

 climate. The stomata are perhaps not so well protected as 

 those in Rhododendron., but on the other hand we have here 



